1. Field of the Invention
The present invention relates to method and apparatus for making a printing plate.
2. Description of the Related Art
In the case of a printing plate for color printing which is used in printing a newspaper with an offset rotary press, accuracy of the image position on the printing plate must be higher than the accuracy (.+-.0.5 mm., approx.) of the image position on a printing plate for monochromic printing, from the viewpoint of the reference position which is required for positioning and winding these printing plates around a plate cylinder of a rotary press. For the printing plate for color printing the differences between the four colors, that is, yellow (Y), magenta (M), cyan (C), and black (BK) must be set within .+-.30 .mu.m. Accordingly, in the process of recording or depicting an image where the first positioning is required, the printing plate for color printing is depicted or recorded with an image and punched to form positioning notches and holes simultaneously so that the positioning notches and holes can be punched in both lengthwise end portions of the printing plate for color printing. In the subsequent processes where positionings are required, for example, the process of bending the printing plate for color printing with a bending device and the process of winding the printing plate around the plate cylinder of the rotary press, register pins are inserted into these notches. As a result, accurate positioning can be performed and a high precision can be obtained in color printing with the above four colors.
However, in a direct printing plate making system such as a direct plate printing recorder called a DPPR or a digital direct plate printing called a DDPP, after a printing plate coated with an organic photoconductor (hereinafter referred to as an OPC plate material) is subject to the recording process, that is, after it is subjected to a depicting process with a laser beam, this printing plate is, while being conveyed in its lengthwise direction, subject to a developing process with a liquid toner, the heating and fixing process, and then, an etching process in the non-imaging area of the plate. In the developing process, if the OPC plate material has the above-described notches, a developing solution will flow irregularly at the notches in the forward portion in the conveying direction of the OPC plate material, and poor development will occur.
In order to prevent such poor development, for example, if the recorded and notched OPC plate material is conveyed widthwise during the developing process, the length at a right angle to the advancing direction becomes too long. For example, in the case of a printing plate of two pages, its length is about 1,100 mm, and its width is about 400 mm. Accordingly, there is a problem in that it is difficult to uniformly develop the entire OPC plate material lengthwise.
Similarly, in a system for making a photosensitive lithographic printing plate, if a printing plate is not accurately positioned in the printing, i.e., image-recording or depicting, punching, and bending processes, the accuracy of the image position is lowered. There is a problem that may cause a shear between colors in color printing. Also, in this case, the image-recorded printing plate is developed while being conveyed. If this printing plate is also subject to the punching process during the printing or recording process, developing solution will flow irregularly at positioning notches, and the developing process will become unstable.
Further, in a system for making a printing plate for monochromic printing, if a printing plate is subjected to punching notches in an image-recording or depicting process for recording an image on the printing plate, developing solution will flow irregularly at the notches in the subsequent developing process, which will result in poor development in the same manner as the above-described systems.
In view of the above problems, one object of the present invention is to provide a method and an apparatus for making a printing plate wherein the developing solution flows regularly on the printing plate so that a stable developing process can be carried out.
Another object of the present invention is to provide a method and an apparatus for making a printing plate for color printing whereby high precision of color printing can be attained without punching notches and holes for insertion of register pins during the recording process such as depicting.